1. Field of the Invention
The present relates to rotation sensors and, more particularly, to a rotation sensor for use with a shaft which rotates from a start position in either direction and which provides information for the determination of the direction required to return from other positions to the start position.
2. Description of the Prior Art
Apparatus for determining the axial position of a rotary member are well known in the prior art. Applications in which the rotary member has a limited amount of rotation from an intermediate start position in either direction to a limit position are also well known. For example, in radar scanning, it is often desirable to be able to position the antenna in a variety of directions but in order to avoid structures which might lie in the path of the antenna or to avoid continuous rotation, which would then require slip rings to convey the signals to receiving apparatus, shaft rotations of less than, for example one complete rotation from a midpoint or other starting point in either direction may be needed. The apparatus schematically shown in FIGS. 1 and 2 describe such a system. In FIG. 1, a central shaft 10 is mounted for rotation about an axis 12 and may carry a radar antenna (not shown) whose direction is desired to be controlled. For purposes of explanation it will be assumed that the rotation of shaft 12 is desired to be less than two complete rotations (one complete rotation in either direction from a start position proximate to that shown in FIG. 1). A shaft driving means, such as motor 20, receives an input shown as arrow 22, which may be a manual input or the input derived by a computer or the like, and operates to drive shaft 10 clockwise or counter clockwise around axis 12 by means of a mechanical connection shown as dashed line 24.
Connected to shaft 10 and movable therewith is a first arm 30 which is shown in FIG. 1 as a sector but which may be of any configuration desired. As shaft 10 rotates under the direction of motor 20, arm 30 will move about axis 12 so that its remote end describes a circle shown by dashed line 32.
A second arm 40, also shown as a sector but which also may be of any desired configuration, is shown in FIG. 1 to be mounted for independent rotation about axis 12 i.e. it is not connected to be driven by shaft 10. The remote end of arm 40 moves in a circle shown as dashed line 41 and is normally free to move in either direction but includes edges 42 and 43 which extend into the path of arm 30 so that as arm 30 rotates, for example in the clockwise direction, an edge 44 of arm 30 will move into a contact with edge 42 of arm 40 and will thereafter drive it in the clockwise direction. Similarly, when driven in a counterclockwise direction, an edge 46 of arm 30 will move into a contact with edge arm 43 (as it is shown in FIG. 1 ) and will thereafter drive arm 40 in a counterclockwise direction. In FIG. 2 it is seen that arm 30 has moved in the counter clockwise direction to push arm 40 into a position approximately 180 degrees from its position in FIG. 1. This angular position may be measured by any convenient means such as a tachometer or other angle sensor 50 connected to motor 20 by a connection shown as dashed line 52.
In order to prevent rotation of shaft 10 beyond certain predetermined limits, stop members 60 and 62 may be fixedly mounted to a frame and extend into the path 41 of arm 40. Members 60 and 62 are shown carrying switches 64 and 66 to provide signals on output conductors 70 and 71 or 72 and 73 respectively when arm 40 reaches the stop members 60 and 62. Stop members 60 and 62 also are shown carrying springs 74 and 76 respectively to prevent accidental operation of switches 60 and 62 by a freely moving arm 40 before being driven there by arm 30.
As arm 30 turns counter clockwise from the position shown in FIG. 1, and beyond the position shown in FIG. 2, it will drive arm 40 to where it contacts spring 76. Further motion of arm 30 thereafter will cause the end of arm 40 to close switch 66 to send a signal over conductors 72 and 73 to a utilization device such as an indicator or computer (not shown). The utilization device may also be connected to angle sensor 50 to indicate the angular position of shaft 10 and to indicate, when appropriate, the reaching of the counter clockwise limit of rotation provided by switch 66. It may also turn motor 10 off since further clockwise rotation of shaft 10 and arm 20 is prevented by stop member 62. When motor 20 drives in a clockwise direction from, for example, the position shown in FIG. 1, arm 30 will move clockwise through nearly a full turn before the edge 44 of member 30 comes in contact with the edge 42 of arm 40. Thereafter, arm 40 will be driven by arm 30 in a clockwise direction until arm 40 comes in contact with spring 74, compresses it and closes switch 64 sending a signal via conductors 70 and 71 to the utilization device (not shown), to turn off motor 20 and indicate the end of the clockwise rotation of shaft 10.
A difficulty has been encountered with the prior art apparatus shown in FIGS. 1 and 2 when it is desired to determine from any position of the shaft, which direction it must rotate to return to the start position. It can be seen in FIG. 2, for example, that while sensor 50 provides an indication of the angular position (approximately 180 degrees) for shaft 10, it does not know whether this position was reached by clockwise or counter clockwise rotation. Of course, a computer connected to motor 20 could keep track of each and every rotation and its direction but this requires an undesirable amount of memory and is more complicated than desirable.